The effectiveness of non-steroidal anti-inflammatory drugs and specific cyclooxygenase (COX)-2 inhibitors for treatment of arthritis provides clinical evidence that increased prostaglandin (PG) production in joint tissues contributes to symptoms of pain, swelling, and stiffness. PG biosynthesis requires the sequential action of COX and PG synthase enzymes. After stimulation with pro-inflammatory cytokines, there is a preferential increase in PGE2 in many different cell types, including synovial fibroblasts. We demonstrated that increased PGE2 in response to pro-inflammatory cytokines in human primary synovial cells is due to induction of microsomal PGE synthase (mPGES)-1. The overall goal of this proposal is to characterize the role of mPGES-1 and other PGE synthases in eicosanoid biosynthesis in immune inflammatory arthritis. We hypothesize a requirement for mPGES-1 to achieve maximal PGE2 production and a role for mPGES-1-derived PGE2 in shaping the immune inflammatory response. We propose to determine the specific role of mPGES-1 relative to other synthetic enzymes for biosynthesis of PGE2 in human synovial fibroblasts using specific COX enzyme inhibitors and inhibitory RNA (RNAi). We will investigate eicosanoid production pathways in cells from mice deficient for COX-1, COX-2 or mPGES-1. Expression of the COX and PGES enzymes in synovial tissues from patients with arthritis or non-arthritic subjects and their relative subcellular localization will be determined. In addition, we will examine the consequences of mPGES-1 deficiency for innate and acquired immunity in genetically null mice. We will determine eicosanoid and cytokine profiles of macrophages, splenocytes, and dendritic cells in mPGES-1 null mice. We will determine the impact of mPGES-1 deficiency on dendritic cell phenotype and function. We will determine the role of PGE2 on immune versus inflammatory mechanisms of arthritis using the collagen-induced arthritis and K/BxN serum models. These data will provide the scientific basis by which to determine if mPGES-1 is an appropriate target for therapeutic intervention in arthritis.